There are options in the View menu to display proteins in different ways. Normally the Cartoon view is used but somehow your puzzle is showing the Stick view. I just checked and Tutorial Puzzles don't show the View menu for you to change the view. This must be a bug.

You may want to reset the puzzle or close foldit and restart to see if it fixes the problem. If not you may still be able to play the puzzle since it's only one of the many ways to view proteins. Please let us know what happens.

Right,when I play intro puzzles I couldn't see view menu,and so I counldn't change.Then I check science puzzles,I can find view menu and am able to use cartoon view.But every time I use rubber band it go back to stick view and I have to set again.